Effectiveness of coronavirus disease 2019 (COVID-19) original vaccines to prevent COVID-19-related hospitalisations among Alaska Native peoples, January 2021-October 2022.

American Indian/Alaska Native (AI/AN) peoples experienced some of the highest rates of coronavirus disease 2019 (COVID-19) disease in the United States. However, there are limited data on COVID-19 vaccine effectiveness in this population. We performed a test-negative case‒control study using electronic health record data to evaluate the effectiveness of the original three FDA-authorised vaccines to prevent COVID-19-associated hospitalisations among AI/AN adults during 2021-2022. COVID-19 vaccines were effective in preventing COVID-19-associated hospitalisation, intensive care unit admission, mechanical ventilation and death in this population. However, vaccine effectiveness waned over time and during the post-Omicron variant time period. Booster vaccination proved effective during a period when the Omicron variant was circulating. Waning effectiveness with time and the introduction of new variants supports the need to stay up-to-date with SARS-CoV-2 vaccination. Evaluating vaccine effectiveness using electronic health records proved to be a useful tool during a pandemic.